The present invention is concerned with precise measurement of physical phenomena, properties or conditions, such as values of capacitance, inductance, or resistance, for example, and is more particularly concerned with apparatus and methods for determining position and movement of a hand or other object in a sensor field.
Douglas Engelbart""s invention of the mouse, patented in 1970, and the parallel development of the graphical user interface, made it possible for persons unfamiliar with computers to quickly become comfortable with their use. These two developments have contributed greatly to the explosive growth of the personal computer industry. More recently, along with hypertext, these innovations have fostered the dynamic growth of the Internet.
Numerous other devices now exist which generally duplicate the functions performed by the mouse and its buttons. These include the touchpad, used to integrate mouse functions into laptop and notebook computers; the joystick and other input devices used primarily with video games; and touchscreen and pen-based techniques which allow direct physical interaction between a user and the objects displayed on a computer monitor screen. All of these are variants of the basic mouse concept; hence, none represents a major breakthrough in human-computer input technology. Meanwhile, three dimensional computer representations are becoming increasingly commonplace in computer-aided design, games, virtual reality and autostereoscopic (i.e., 3D without glasses) displays. Existing two-dimensional input devices are inadequate to function as a natural, user-friendly complement to these three-dimensional output systems.
Existing two-dimensional input devices are tactile, requiring physical contact and manipulation by the user. The mouse, for example, is subject to failures from wear, jamming from foreign materials, and slipping on smooth surfaces. Other mouse-like devices, due to their tactile nature, suffer similar problems from repeated use and physical abuse.
In many types of computer use, the user constantly moves back and forth between the keyboard and the mouse or touchpad. These actions waste motion, are time consuming and often result in keystroke errors when the user""s hand returns to the keyboard.
More recently, three-dimensional computer input techniques have been proposed, using video cameras or an arrangement of active devices, including sonic, radio frequency or infra-red emitters and detectors. Such techniques are costly, complex and usually intrude on the user""s freedom of movement.
The present invention provides high-precision apparatus, systems, and methods that employ phase shifts in a fixed-frequency signal. For example, the invention can be used to determine the position and motion of a hand or other object in a sensor field using one or more conducting elements or probes. It can also be used, for example, in precise measurement of electrical properties, such as capacitance, inductance, or resistance. In its application to the measurement of the position and motion of a hand or other object, human body capacitance1 is transferred to the apparatus by the presence of a hand or other object near a probe or probe array. A multi-dimensional computer input is achieved by means of an array or network of two or more probes. In a preferred embodiment, probes are arranged in opposing pairs to achieve improved sensitivity and to cancel sensor nonlinearity.
1 See xe2x80x9cHuman Body Capacitance: A Reviewxe2x80x9d by Albert E. Seaver, Proceedings of the 25th Annual Meeting, Electrostatics Society of America, pp. 16-29, 1997. 
In a preferred embodiment for the measurement of a hand or other object in a sensor field, a fixed-frequency signal is applied to a sensor network comprising one or more pairs of conducting elements connected to one or more passive components such as fixed resistors and/or inductors. Sensed capacitance changes result in phase changes in the applied signal relative to a reference signal. A novel method of phase measurement measures these phase changes with extremely high resolution and accuracy, producing an output that is inherently digital (i.e., incremental), and that can be readily converted into any desired computer input format.
Probe geometry can be varied to meet an unlimited number of specific applications. For example, multiple independent arrays can be employed to achieve a six-degree-of-freedom control input by using each hand to control a separate three-axis array, or by two persons competing simultaneously in the same 3D video game. Multiple planar arrays can be used to sense the proximity or actual location of a person or object for safety or intrusion detection purposes.
The present invention provides, inter alia:
1) A novel apparatus and method of measuring minute capacitance values with extreme precision, thereby to produce computer inputs representing the position and motion of a hand or other object in three dimensions,
2) A computer input device with no moving parts, which can be operated without physical contact, and is therefore inherently more reliable than existing tactile and force-feedback input devices,
3) A computer input device that permits a person using both a keyboard and the present invention to alternate between the two without moving their hands away from the immediate vicinity of the keyboard, thereby reducing fatigue and increasing the user""s speed and accuracy,
4) A computer input device whereby human gestures can be compared to stored profiles that represent commands or data inputs to a computer or control system,
5) A low-cost computer input device,
6) A completely non-intrusive computer input device,
7) A computer input device which, in one embodiment, can be plugged into the mouse port of a desktop computer, obtaining its operating power directly from the host computer.
8) Apparatus and methods for precise measurement of unknown electrical properties, such as capacitance, inductance, and resistance.
9) Apparatus and methods for precise measurement of phenomena, properties or conditions that produce minute phase shifts in a fixed-frequency signal.